Controlled rectifier and battery charger



Jan. 27, 1942. w. P. OVERBECK 2,270,894

CONTROLLED RECTIF IER AND BATTERY CHARGER Filed Jan. 29, 1938 3Sheets-Sheet l lilllb l'll'llllil W/L cox P OVERBECK Jan. 27, 1942. P,OVE BECK 2,270,894

CONTROLLED RECTIFIER AND BATTERY CHARGER Filed Jan. '29, 1938 3Sheets-Sheet 2 w/Lcox POI/ERBECK Jan. 27, 1942.

w. P. OVERBECK 2,270,894

CONTROLLED RECTIFIER AND BATTERY'CHARGER .5 Sheets-Sheet 3 Filed Jan.29, 1938 Z era Axis W/LCOX P OVERBECKI 59 *s i *2 1 i Q 5 1 1 i I I Nload Car/e225 1A [law/222v load Current b A ry,

Patented Jan. 27, 1942 CONTROLLED RECTIFIER, AND BATTERY CHARGER WilcoxP. Overbeck, Waltham, Mass., assignor to Raytheon Manufacturing Company,Newton, Mass, a corporation of Delaware Application January 29, 1938,Serial No. 187,673

12 Claims.

This invention relates to controlled rectifiers which may be used for avariety of purposes, including the charging of batteries.

One of the objects of my invention is to devise a system for controllingelectrical space discharge rectifiers so that the output thereof ismaintained at a constant value throughout the entire load range of saidrectifiers.

Another object is to provide such a system in which the value of thevoltage so maintained may be selected and varied at will.

A further object is to devise such a system which is very stable inoperation.

A still further object is to provide such a controlled rectifier systemwhich automatically charges a battery and varies its charging rate in adesired manner as the charge of said battery and the load thereonchanges.

An additional object is to accomplish all of the above by the use ofmagnetically-controlled gaseous discharge rectifiers.

The foregoing and other objects of m invention will be best understoodfrom the following description of exemplifications thereof, referencebeing had to the accompanying drawings, wherein:

Fig, l is a circuit diagram illustrating one embodiment of my invention;

Fig. 2 is a circuit diagram embodying my invention in an automaticbattery-charging sys tem;

Fig. 3 represents the varying currents flowing through different partsof my control circuit;

Fig. 4 represents various voltages and fluxes flowing in m novel system;

Fig. 5 shows a series of curves representing the characteristics of thesystem as illustrated in Fig. 1; and

Fig. 6 shows a series of curves representing the characteristics of thearrangement as illustrated in Fig. 2.

In Fig. 1 there is represented a single-phase full-wave rectifyingsystem comprising two rectifier tubes I and 2. These tubes arepreferably of the magnetically-controlled type as more fully describedin the patent to Percy L. Spencer, No. 2,124,682, dated July 26, 1938,for an improvement in Electrical gaseous discharge devices. Each tube isprovided with an indirectly-heated cathode 3 of the type which may beheated to temperature of thermionic emission during operation, and ananode 4. Intermediate each cathode 3 and anode 4 is interposed anauxiliary electrode 5 which may consist of an electrically-com ductingcylinder, either perforate or imperforate.

Instead of completely surrounding the discharge space, the auxiliaryelectrode 5 may partially surround it. Each tube is filled with asuitable ionizing gas or vapor, preferably argon, with a pressure of theorder of one millimeter or less. In any event, the gas pressure is of asuitable value so that when a discharge occurs between the cathode andanode, the gas or vapor becomes ionized and current flows at arelatively low voltage drop. Each cathode 3 is provided with a heatingfilament I, one end of which is directly connected to its associatedcathode. Each auxiliary electrode 5 is connected by means of a conductor8 to the opposite end of its associated heating filament I. Theintermediate electrode 5 may be connected in any other desired manher,for example directly to the cathode 3, and a suitable bias voltage maybe impressed upon each auxiliary electrode 5, if desired. In order tocontrol the starting of the current between each cathode 3 and anode 4,a control winding 8 wound upon the magnetic core is disposed externallyto the rectifier tubes I and 2. The magnetic core is constructed asdescribed in the Spencer patent referred to above so as to impress amagnetic field transverse to the discharge path between each cathode andanode within the auxiliary electrode 5. In the interest of simplicitythe transverse relationship is not illustrated in the drawings, but thewinding 8 and its associated core are indicated in a purely diagrammaticmanner.

In order to supply the rectifier tubes I and 2 with power, the anodes 4are connected to the opposite ends of a secondary winding 9 of atransformer II) which has a primary winding I I. The two cathodes 3 areconnected together by means of a conductor I2 which thus constitutes thepositive terminal of the output of the rectifiers I and 2. A tap I5intermediate the ends of the secondary winding 9, preferably at thecenter point thereof, constitutes the negative terminal of the output ofthe rectifier tubes I and 2. A conductor I6 is connected to said centertap I5. In order to remove the ripples from the rectified output of thetubes I and 2, a filter consisting of filter chokes I3'and I4 in seriesfrom the positive terminal lead I2 and filter condensers I1 and I 8connected from opposite sides of the filter choke I4 to the negativeconductor I6 are provided. A conductor I2 extends from the outer end ofthe choke I4 and a conductor I6 extends from the negative lead I6. Thetwo conductors I2 and I6 extend to the terminals III which constitutethe direct current output terminals of the controlled rectifier system.In order that the direct current output voltage may be readily observed, an output voltmeter is connected between the conductors l2 andIS. A fuse l9 may be interposed in the lead H.

In order to supply the heating filament I with heating current, there isprovided a transformer 22 having a secondary 2| and a primary 23. Thesecondary 2| is provided with a center tap 25 from which a conductor 24extends to the common cathode lead I2, and thus to one side of each ofthe filaments 1. A conductor 26 extends from one end of the secondary 2|to the outer end of one of the filaments 1, and a conductor 21 extendsfrom the other end of the secondary 21 to the outer end of the otherheating filament 1. Due to the heating circuit arrangement as described,a balanced heating current flows in the two filaments 1 and the voltageconditions on each of the controlled rectifier tubes l and 2 aresymmetrical.

In order that the output voltage from the rectifier system describedabove be maintained at a constant value with substantially no deviationtherefrom, I provide a constant reference voltage against which theoutput voltage of the rectifier system is balanced. The constantreference voltage may be obtained from a full-wave rectifying systemcomprising a rectifier tube 28. This tube contains an indirectly-heatedthermionic cathode 29 and two anodes 30. The cathode 29 is raised totemperature of thermionic emission by means of a suitable heatingfilament 31. The rectifier tube 28 is supplied with power from thesecondary winding 32 of a transformer 33 which has a primary winding 34.The two anodes are connected to the outer ends of the secondary winding32. A conductor 35 is connected to the cathode 29 and serves as thepositive reference voltage lead. The secondary 32 is provided with anintermediate center tap 31 to which is connected a conductor 36 whichforms the negative reference voltage supply lead. A smoothing condenser38 is connected directly across the two leads 35 and 36, and eliminatesto a substantial degree the ripples from the rec tified current outputof the rectifier 2B. In order to maintain the reference voltage constantwithin very narrow limits, a glow discharge voltage regulating tube 39is likewise connected be tween the two conductors 35 and 36. The tube 39is of the type which contains relatively extended electrodes whichremain cold throughout its operation and which is filled with anionizale inert gas. In such a tube current is conducted between theelectrodes by the glow dis charge phenomenon which has the property ofmaintaining between the electrodes a very constant voltage for allvalues of current flowing through said tube below a predeterminedmaximum. In order to absorb variations in voltage which may occur at theoutput terminals of the rectifier tube 28, a resistance 40 is connectedin the positive supply lead 35 ahead of the voltage regulating tube 39.Across the terminals of the voltage regulating tube 39 which maintains aconstant reference voltage as described above, is connected apotentiometer 41. The potentiometer 4| is provided with a movablecontact 42, whereby any desired part of the total reference voltage maybe selected.

It will be noted that the controlled rectifying system is of the typehaving an input choke I3 to the filter. The total input inductance tothe filter is always greater than the critical value at which currentflows through each rectifier tube I and 2 for a complete half cycleafter a discharge has been initiated therein. A potentiometer resistance43 is likewise connected across the output of the controlled rectifiersystem comprising the rectifier tubes l and 2. This resistance 43prevents the total resistance conneoted to the output of the rectifiertubes l and 2 from exceeding a predetermined value. The criticalinductance and its relation to the output resistance of such acontrolled rectifier system as I have described are more fully describedand claimed in my copending application, Serial No. 186,372, filedJanuary 22, 1938, for an improvement in Filter systems for controlledrectifiers.

In order to tie the controlled rectifier system to the reference voltagesystem, a resistance 44 is connected from the contact 42 on thepotentiometer 4| to the upper end of the resistance 43. Since verylittle, if any, current flows through the resistance 44, it may be of acomparatively high value. It is desirable that the current through theresistance 43 shall be maintained at a substantially constant value. Inorder to accomplish this, an adjustable contact 45 is provided on theresistance 43, and is connected to the upper end thereof. Likewise thecontact 45 is tied physically to the contact 42 so that they both movetogether. This relationship is indicated diagrammatically by the dottedline connecting the two contacts 45 and 42. In this way, as the contact42 is adjusted to provide for a lower output voltage, the contact 45decreases the resistance 43 so that the resultant current flowingthrough the resistance 43 remains substantially constant.

As pointed out in my copending application referred to above, wLc/Rincreases as the delay in the firing of the rectifiers increases. Thesymbol to represents 211' times the frequency of the A. C. power line,Le represents the critical inductance to which I have referred, and Rrepresents the value of the resistance connected across the outputcircuit. Since the load connected to the terminals 19 may at some timebe disconnected, R may be considered the resistance of 43 for purposesof determining the value of the critical inductance Le. As the directcurrent output voltage across the terminals I9 is decreased byadjustment of the contact 42, as pointed out below, the time of firingof the tubes I and 2 will be delayed. If the resistance 43 werepermitted to remain the same under all conditions, it would then benecessary to have a greater value of critical inductance at lower valuesof output voltage. However, by the adjustment of the contact 45 with thecontact 42 as described above, the resistance 43 is decreased as theoutput voltage is decreased, and thus the necessary value of thecritical inductance remains substantially the same for all values ofoutput voltage. Furthermore, by this arrangement, a comparatively highvalue of resistance 43 may be used at the higher output voltages, thuspreventing any excess loss of power in said resistance 43.

If during operation the voltage across the output of the controlledrectifiers l and 2, namely the voltage which appears across theresistance 43, differs from the voltage appearing between the contact 42and the negative reference voltage supply lead 36, this difference involtage will appear between said negative lead 36 of the referencevoltage system and the negative lead 16 of the controlled rectifiersystem. This voltage dilference is then utilized to vary the voltageoutputof the controlled rectifiers and Zso as to bring said outputvoltage into substantial bal-- ance with the voltage appearing betweenthe contact 42 and the negative supply lead 36 of the reference voltagesystem. Thus, by adjusting the contact 42, the voltage at which theoutput from the controlled rectifiers I and 2 is maintained may readilybe selected.

The voltage difference between the two systems as described above isamplified before itis utilized to control the rectifiers and 2. For thispurpose a voltage-arnplifying tube 46 is provided. This tube ispreferably of the pentode type having an indirectly-heated thermioniccathode 41,

a control grid 48, a screen grid 49, a suppressor grid 5|), and an anode5|. Thecathode 41 may be heated to temperature of thermionic emission bya suitable filamentary heater 52. The output voltage from the rectifier28 is utilized to supply power to the amplifier tube 46. For thispurpose a conductor 53 extends from the negative terminal of thepotentiometer 4| to the cathode 41, and the anode 5| is connectedthrough the resistance 54 and conductors 55 and 56 to the positiveterminal of the potentiometer 4|. The control voltage difference isimpressed upon the control grid 48 by having the negative terminal ofthe resistance 43 connected through a resistance 51 to said controlgrid. As is customary in tubes of the pentode type, the suppressor grid50 is connected back to the cathode 41 by means of a conductor 59. Inorder to provide the screen grid 49 with suitable intermediatepotential, a resistance 6| is connected across the reference voltagesupply system, and a conductor 59 connects the screen grid 49 to anintermediate tap 60 on said resistance 6|. When the voltage on thecontrol grid 48 varies, the current in the anode circuit likewisevaries, and an amplified voltage drop appears across the anoderesistance 54. In order to make the system stable and prevent hunting,the response of the amplifier tube 46 to variations in the controlvoltage is delayed.

This is accomplished by connecting a condenser L) 52 between the contact42 and the control grid 48. Additional delay producing a degeneratingeffect in the amplifier tube 46 is accomplished by means of a condenser63 connected between the control grid 48 and the anode 5|. densers 62and 63 are of such a value that the delay in the response of theamplifier tube 46 is of the same order of magnitude as the delay in thechange of the output voltage upon the supplying of controlling currentsto the regulating coils 8. Preferably the delay in the amplifier tube 46is somewhat greater than said delay in the controlled rectifier tubesystem.

In order to supply the tube-controlling coils 8 with power, a Vacuumtube rectifier 84 controlled from the amplified voltage appearing acrossthe resistance 54 is used. The rectifier 64 is provided with afilamentary thermionic cathode 65, an anode 56, and a control grid 51.The cathode 65 is connected directly to the outer end of the resistance54, and the grid 61 is connected by means of the conductors 68 and 69 tothe other end of the resistance 54. In this way the amplified controlvoltage is impressed upon said grid.

In order to supply the rectifier tube 64 with power, a transformer 1|having a secondary winding 16 is provided. A phase-shift networkconsisting of a resistance T2 in series with a condenser 13 is connectedacross the secondary winding 18. The resistance 12 and the condenser 13The con- H may be made adjustable, but in the interest of simplicity,the resistance 12 itself is designed so that some adjustment may be hadtherein. The secondary winding 10 is provided with a center tap l5 fromwhich a conductor 14 extends to the conductors 55, and thus to thecathode 65. A conductor 16 extends from the point interme diate theresistance 12 and the condenser 13 to one side of the two control coils8 connected in parallel. A conductor 1'! extends from the other side ofsaid coils 8 to the anode 66. A condenser I8 is connected in parallelwith the two control coils 8, and is preferably of such a value as tomake the circuit of said control coils resonant at the supply voltagefrequency.

In order to supply the filament 65 with heating current, the transformerH has an auxilary secondary winding 19. One end of said secondary isconnected by means of a conductor 88 to one end of the filament 65. Theother end of said secondary I9 is connected by means of the conductors8i and 55 to the other side of saidfilament 65.

In order to supply the heating filaments 52 and 3| with current, anadditional secondary winding 62 is also provided on the transformer H,The opposite ends of said secondary 82 are connected by means of theconductors 83 and 34 to the opposite ends of said heating filament 3|.Two conductors 85 and 86 connect the opposite ends of the filament 52 tothe conductors 83 and 94, respectively, thus supplying said filamentwith current from the secondary 82. The transformer 1| is energized bymeans of a primary winding 81.

The entire system is supplied with power from a pair of alternatingcurrent input terminals 89. To one of these terminals is connected analternating current line conductor 98; the other input terminal isconnected through a main switch 9| and a fuse 92 to the otheralternating current line conductor 93, The primary windings 23 and 81are connected directly across the conductors 96 and 93. Thus when theswitch 9| is closed, all of the filaments are supplied with heatingcurrent. It is desirable that the application of the anode voltages inthe respective tubes should be delayed until the cathodes have beenheated to their operating temperature. For this purpose the time delayswitch 95 is provided. A conductor 94 extends from the line conductor tothe time switch 95, the other side of which is connected to a conductor96 extending to an additional conductor 91. The conductor 91 isconnected to one end of the primary winding II and also to one end ofthe primary winding 34. The other end of the primary winding I isconnected directly to the line conductor 93, and the other end of theprimary winding 34 is also connected by means of the conductor 98 to theline conductor 93. When the switch 9| is first closed, the time delayswitch is open and does not close until a predetermined interval of timeduring which the respective cathodes have been raised to their operatingtemperature. After said interval of time, the time delay switch 95operates to connect the conductors 94 and 96, thus energizing theprimary windings II and 34 which supply power to the anodes of therespective tubes of the system.

The constants of the system described above are so selected that thecontrol grid 61 of the rectifier tube 64 normally has impressed upon ita negative voltage which permits the tube 64 to conduct pulses ofcurrent only at the positive peak of the voltage impressed upon theanode 66. Under these conditions, as shown in Fig. 3, pulses of currentIr will flow through the output circuit of the rectifier circuit 64.These pulses of current are supplied through the conductor 11 to thecontrol coils 8 connected in parallel with the resonating condenser 16.When said parallel circuit is energized by the pulses of current Ir, analternating sine wave current will flow in said parallel circuit. Underthese conditions, a current Ic will flow through each control coil 8.Since each control coil 8 may be considered as a pure inductance, thecurrent will lag the current impulses Ir by 90 degrees, as indicated inFig. 3. As indicated in Fig. 4, two voltages E1 and E2 180 degrees outof phase with each other, are impressed upon the tubes l and 2respectively, The transverse magnetic flux set up by the coil 8associated with each controlled rectifier prevents the starting ofcurrent whenever the anode of such tube is positive until said flux hasfallen below a predetermined minimum value. This minimum value variessomewhat with the voltage on the anode. The curve F in Fig. 4 representsa possible flux characteristic curve for such tubes. Whenever the fluxis less than the value indicated by the curve F, the tube will start toconduct current. Since the flux through each coil 8 is in phase with thecurrent flowing through said coil, when the current In flows througheach coil 8, a flux m, as indicated in Fig. 4, will be set up across thedischarge path of each rectifier tube I and 2, The flux 1 drops belowthe curve F at the point X during the time when E1 is positive. Thus thetube I starts to conduct current at that point, and the conduction ofcurrent continues until the flux 1 intersects the curve F at the point Yduring the time that the voltage E2 is positive, At the point Y,therefore, the tube 2 will start to conduct current and the tube I willcease its conduction of current. It will be noted that, as indicated inFig. 4, each tube conducts current for a full half cycle. This occurswhen the input choke l3 has an inductance greater than the criticalvalue as described and claimed in my copending application referred toabove. Under the conditions described, a voltage as represented by thesolid line E1 E2 appears between the conductors l2 and Hi. Thenon-conducting portions of the two voltage waves E2 and E1 arerepresented by the dotted lines. The filter consisting of the coils l3and I4 and the condenser l1 and I8 smooths out the voltage waveappearing between the conductors l2 and I6 resulting in an average valueof voltage represented by the line Ede.

If the voltage across the resistance 43 tends to rise above thereference voltage on the potentiometer 4|, the grid 48 of the tube 46tends to become more negative, thus decreasing the current flow throughthe resistance 54 and making the grid 61 of the tube 64 less negativewith respect to its cathode. Under these conditions, the pulses ofcurrent I1- supplied by the tube 64 increase in magnitude, and thuscause currents of increasing amplitude to flow through the coils 8, Thusas the voltage output across the resistance 43 increases, increasingvalues of flux (in, m and 3, as indicated in Fig. 4, may be set up inthe respective tubes I and 2. Since these curves of flux intersect thecurve F at increasingly delayed points along the voltage waves E1 andE2, conduction will occur at increasingly delayed points on said voltagewaves. As the initiation of conduction is delayed on the voltage wavesE1 and E2, the resultant D. C. voltage will become less. Thus anyincrease in the voltage across the resistance 43 sets the system inoperation to decrease the voltage output from the tubes l and 2, andthus decreases the voltage across the resistance 43. It will beunderstood that if the voltage across the resistance 43 tends to becomeless than the selected portion of the reference voltage, the system willwork in the opposite direction from that described above, and will tendto raise the voltage across the resistance 43 until it again equals theselected portion of the reference voltage. From the foregoing it will beseen that the system operates so as to maintain the voltage across theresistance 43 substantially equal to Whatever portion of the referencevoltage across the potentiometer 4! is selected by the adjustable tap42,

In Fig. 5 are given typical characteristic curves of a system such as Ihave described above. By providing the potentiometer 4| with a number ofdefinitely located taps, the characteristic curves A, B, C, D and E maybe obtained. It wil1 be noted that each of these curves gives a constantoutput voltage for variations in load This is due to the fact that thesystem described maintains the output voltage of the controlledrectifier system equal to the reference voltage no matter what type ofvariation, whether due to load or otherwise, is introduced into thesystem.

My invention is also readily applicable to automatic battery chargingsystems, and may be applied thereto, for example, as shown in Fig. 2. InFig. where the arrangements as shown in Fig. l are identical, the samereference numorals are applied to the various parts as in l. The systemas shown in Fig. 2 differs from Fig. 1 only in the output circuit of thecontrolled rectifiers l and 2. In Fig. 2 a bat tery 953 is connecteddirectly across the output terminals l9. Also a load IUD connectedacross said terminals ii! is also indicated. Since the battery 99 inFig. 2 serves in itself as a filter element and tends to remove ripplesfrom the output voltage, the filter system as shown in Fig. l iseliminated. In Fig. 2, however, a choke IEH is connected in series withthe output from the positive terminal conductor I2. The choke I01 is ofsuch a value as to exceed the critical inductance value as discussedabove in connection with the choke l3. Also in series with the choke 101are a plurality of parallel resistances H12, Hi3 and NM. The resistancesHi3 and I04 are provided with switches I05 and H16 so that they may beselectively connected into the circuit. In this way the amount ofresistance connected in series with the load and battery in the outputof the controlled rectifiers l and 2 may be adjusted. The voltageregulating glow discharge tube 39, which is preferably used in suchsystems, may have a voltage drop of the order of volts. The battery 99,however, may have a voltage of volts when fully charged. Therefore,instead of comparing the entire voltage of the battery with thereference voltage, a portion of said voltage may be selected by means ofa tap U31 on the resistance 43. In this way, any predetermined part ofthe battery voltage is compared with the selected portion of the referonvoltage. A resistance I08 analogous to the res .nce M of Fig. 1 connectsthe tap ID! to the ta 52 in Fig. 2.

In the system described above, the tap 42 is adjusted along thepotentiometer 4! until a voltage is selected which is the voltage atwhich the battery 99 should be maintained. With the load set atsubstantially its zero value, very little current is drawn from thesystem. Under these conditions the system operates to maintain thevoltage of the charging system at the desired battery voltage, whereuponthe proper trickle charge rate is supplied to the battery 99 to maintainit at said voltage. curves as shown in Fig. 6, the system under theseconditions will operate on the horizontal line F very close to thevertical axis. If we assume that the switches I05 and I66 are in theiropen position and the load I is adjusted so as to draw increasing valuesof current, such increased currents will flow through the resistance I02and tend to lower the voltage supplied from the rectifiers l and 2 tothe battery 59. However, the regulating system will operate to maintainthe output voltage at the requisite value, and under these conditionssubstantially all of the current supplied to the load will be drawn fromthe rectifiers l and 2. However, as the load current increases, thecontrol system will cause the rectifiers I and 2 to fire earlier in theconducting cycle until the tubes I and 2 reach a condition in whichconduction starts whenever the anode 4 becomes positive. This conditionrepresents the maximum voltage output which can be supplied by thereotifiers l and 2, and beyond that point no additional regulation canbe secured. If the load further increases, the voltage output from thecontrolled rectifiers will tend to drop along the line A of Fig. 6.Under these conditions, the excess current is no longer supplied by thecontrolled rectifiers I and 2, but is furnished to the load from thebattery 99. However, the controlled rectifiers I and 2 still continue tosupply their maximum current rating. If the load is again decreasedbeyond the excess value, the battery no longer supplies current butfloats across the output, and is automatically maintained in its fullycharged condition.

If it is desired to increase the maximum cur.- rent which the controlledrectifiers will supply to the load, the switch Hi5 may be closed, whichthen decreases the resistance in series with the output from therectifiers. Under these conditions, a greater value of load current mustbe drawn from the rectifiers in order to produce a voltage drop whichwill bring the regulation of the rectifiers to its maximum value. Underthese conditions the load current drawn from, the controlled rectifierswill continue along the line F in Fig. 6 until the curve B is reached,at which point the controlled rectifiers l and 2 will refuse to supplyany more current to the load, and the excess will be furnished by thebattery. Likewise, closing the switch I66 will enable the controlledrectifiers l and 2 to supply current up to the point where the droopingcharacteristic 0 occurs. The dotted line continuations of curves A, Band C represent the type of characteristic which a rectifier would haveif it were not provided with automatic regulation. The slope of each ofthe curves A, B and C depend upon the total value of resistance inseries with the output of the controlled rectifiers. As the amount ofresistance is decreased, the slopeof the curve will decrease, thuspermitting larger values of output current from the controlledrectifiers as described above.

The automatic battery charging system described above furnishes to theload I00 very good dynamic regulation so that the voltage at the load ismaintained at constant value for wide In the characteristic variationsin load requirements. Furthermore, the arrangement greatly increases thelife of the battery because the battery is called upon only to supplyexcess load requirements and at other times is automatically maintainedon a trickle charge to keep the battery at its rully charged condition.

Of course it is'to be understood that this invention is not limited tothe particular details as described above inasmuch as many equivalentswill suggest themselves to those skilled in the art. For example,certain aspects of my invention might be utilized with any type ofcontrolled rectifier tube in which the discharge may be initiated at anydesired portion of the positive voltage wave applied to the anode,whereupon conduct-ion will continue as described in connection with thisinvention. Such controlled rectifier might be of the grid-controlledtype or of some other magnetically-controlled type. Also other types ofreference voltage systems may be utilized. These and other equivalentswill present themselves, and therefore it is desired that the appendedclaims be given a broad interpretation commensurate with the scope ofthe invention withinthe art.

What is claimed is:

l. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, a control circuit, control means for controlling the output ofsaid rectifier in response to current flowing in said control circuit,and means for supplying discontinuous current pulses to said controlcircuit at the frequency of said alternating current source, saidcontrol circuit comprising an inductance and a capacity in parallel of avalue whereby a substantially sine wave alternating current of thefrequency of said alternating current source flows in said controlcircuit when said current pulses are supplied to said control circuit.

2. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, a control circuit, control means for delaying the firing ofsaid rectifier in response to current flowing in said control circuit,and means for supplying discontinuous current pulses to said controlcircuit at the frequency of saidalternating current source, said controlcircuit comprising an inductance and a capacity in parallel of a valuewhereby a substantially sine wave alternating current of the frequencyof said alternating current source flows in said control circuit whensaid current pulses aresupplied to said con- .trol circuit.

3. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed betweensaid'circuits, a control circuit, electromagnetic control means fordelaying the firing of said rectifier in response to current flowing insaid control circuit, and means for supplying discontinuous cur,- rentpulses to said control circuit at the frequency of said alternatingcurrent source, said control circuit comprising an inductive energizingwinding for said control means and a capacity in parallel, whereby analternating current of the frequency of said alternating current sourceflows in said control circuit when said current pulses are supplied tosaid control circuit. 1

4. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, a control circuit, control means for controlling the output ofsaid rectifier in response to current flowing in said control circuit,means for supplying discontinuous current pulses to said control circuitat the frequency of said alternating current source, said controlcircuit comprising an inductance and a capacity in parallel of a valuewhereby a substantially since wave alternating current of the frequencyof said alternating current source flows in said control circuit whensaid current pulses are supplied to said control circuit, and means forvarying the amplitude of said current pulses in accordance with adesired controlling variation, whereby the amplitude of the currentflowing in said control circuit is varied.

5. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, a control circuit, control means for controlling the output ofsaid rectifier in response to current flowing in said control circuit,means for supplying discontinuous current pulses to said control circuitat the frequency of said alternating current source, said controlcircuit comprising an inductance and a capacity in parallel, whereby analternating current of the frequency of said alternating current sourceflows in said control circuit when said current pulses are supplied tosaid control circuit, a reference direct current voltage supplyassociated with the output of said rectifier, means responsive to thedifference between the output voltage of said rectifier system and saidreference voltage, and means for controlling the amplitule of saidcurrent pulses in accordance with said difference.

6. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, a control circuit, control means for controlling the output ofsaid rectifier in response to current flowing in said control circuit,21. reference direct current voltage supply associated with the outputof said rectifier, means responsive to the difference between the outputvoltage of said rectifier system and said reference voltage forsupplying a controlling current to said control circuit, and means fordelaying the response of said last-named means to substantially the samedegree as the change in output voltage trolling the output of saidrectifier in response 8. A rectifier system comprising an alternatingcurrent supply circuit, a direct current output circuit, a rectifierinterposed between said circuits, a control circuit, electromagneticcontrol means for delaying the firing of said rectifier in response tocurrent flowing in said control circuit, a control rectifier forsupplying discontinuous current pulses to said control circuit at thefrequency of said alternating current source, means for supplying analternating voltage of the supply source frequency to said controlrectifier, means for shifting the phase between said supply circuitvoltage and the voltage supplied to said control rectifier, said controlcircuit comprising an inductive energizing winding for said controlmeans and a capacity in parallel, whereby an alternating current of thefrequency of said alternating current source flows in said controlcircuit when said current pulses are supplied to said control circuit,and means for controlling said control rectifier to vary the amplitudeof said current pulses in accordance with a desired controllingvariation.

9. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, said rectifier comprising a plurality of rectifying phases,control means for delaying the firing of each of said rectifier phases,an input inductance interposed in series between said rectifier and saidoutput circuit, a resistance connected across said output circuit, meansfor varying the time of delay of firing of said rectifier phases forvarying the output voltage, and means for varying said resistance sothat it decreases with an increase in the time of delay of said firing,said inductance being of the critical value or greater at whichconduction occurs through each rectifier tube after firing until theadjacent rectifier tube fires.

10. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, a control circuit, control means for controlling the output ofsaid rectifier in response to current flowing in said control circuit,means for supplying discontinuous current pulses to said control circuitat the frequency of said alternating current source, said controlcircuit comprising an inductance and a capacity in parallel, saidparallel circuit being tuned to the frequency of said alternatingcurrent source.

11. A rectifier system comprising an alternating current supply circuit,a direct current output circuit, a rectifier interposed between saidcircuits, a control circuit, means for supplying dis continuous currentpulses to said control circuit at the frequency of said alternatingcurrent source, a reference direct current voltage supply associatedwith the output of said rectifier, and means responsive to thedifference between the output voltage of said rectifier system and saidreference voltage for supplying a controlling current to said controlcircuit to reduce said difference.

12. A system comprising a voltage-supplying device, control means forcontrolling the output voltage of said device, a reference voltage,means responsive to the difference between said output voltage and saidreference voltage for supplying a controlling influence to said controlmeans, and means for delaying the response of said lastnamed means tosubstantially the same degree as the change in output voltage is delayedupon the supplying of a controlling influence to said control means orto a greater degree.

WILCOX P. OVERBECK.

